Implementation of Map for use when building model data for use
with UI tools. Supports chained calls and generation of model attribute names.

This class serves as generic model holder for both Servlet and Portlet MVC,
but is not tied to either of those. Check out the Model interface for
a Java-5-based interface variant that serves the same purpose.

addAttribute

Note: Empty Collections are not added to
the model when using this method because we cannot correctly determine
the true convention name. View code should check for null rather
than for empty collections as is already done by JSTL tags.